(J. David Ake/AP)

THE INTERNAL Revenue Service may be the least-loved arm of the federal government. For tax-hating Republican lawmakers still angry over what they see as IRS malfeasance, the antipathy is especially strong. That explains why GOP lawmakers repeatedly have cut the agency’s budget over the past several years, including a 3 percent reduction this year . But no matter how therapeutic it may feel to hack away at the IRS, it is deeply irrational.

IRS Commissioner John Koskinen said Thursday that the budget punishment has been so harsh that he may have to shut down the agency sometime this summer.

Mr. Koskinen’s warning comes on the heels of an ominous report from National Taxpayer Advocate Nina Olson , who represents everyday Americans’ concerns at the IRS. In her annual report to Congress, Ms. Olson described an impending customer service disaster as the agency struggles to do an ever more complex job with less and less money. About half of the 100 million or so people who will try to call the IRS this year probably won’t get through. The agency reckons that even those who do will have to wait 30 minutes or more. Those who tough it out on hold won’t be able to ask anything but basic questions because the agency has limited the topics its taxpayer support staff may answer. The agency will also reduce services at walk-in centers and stop helping elderly Americans fill out their tax forms.

“If these projections prove accurate, taxpayers in 2015 will receive the worst levels of service since the IRS implemented its current performance measures in 2001,” Ms. Olson reported.

If the IRS were overfunded, some cutting back would be justified. But the agency has seen its inflation-adjusted budget reduced by about 17 percent since 2010, Ms. Olson calculated. For 2015, lawmakers tried to keep the taxpayer services budget stable, but they still ended up reducing its inflation-adjusted funding level by 3.8 percent. “The IRS can operate more effectively and efficiently in certain areas,” Ms. Olson concluded. But “the only way the IRS can assist the tens of millions of taxpayers seeking to speak with an IRS employee is to have enough employees to answer their calls.”

The consequences won’t end with taxpayer frustration. Mr. Koskinen has estimated that eroding enforcement will result in the government losing $2 billion from its $346 million cut in IRS funding. IRS dysfunction will also make the implicit tax that Americans pay tax preparers every year even closer to mandatory.

This is, to use the technical term, nuts. Congress should restore IRS funding in the short term, then simplify the tax code in the long term so that it doesn’t take a CPA to navigate the internal revenue system.

It is often said that government should protect people who follow the rules and pay their taxes. Instead, Congress has opted to help tax cheats and the tax preparation industry.